BI266 - roots

Embryo root

the radicle - roots can be retracted back to the embryo or develop from other organs

embryo

the first organ that emerges from the seed

Adventitious roots

develop from other organs like stems or leaves.

Form the basis of propagation using cuttings.

root morphology

• not an articulated organ 

• no nodes and internodes

Root Cap

• produced by the apical meristems

• protects apical meristem

Region of cell division 

hosts three primary meristems

• protoderm

• ground meristem

• procambium

protoderm

produces the epiderm

ground meristem

produces parenchyma in the cortex

Procambium

produces the primary vascular elements 

Vascular elements

xylem and phlolem

primary meristems

produced by the primordial meristem in the root apex

region of elongation

cells do not divide, they elongate.

cells are not differentiated 

Region of maturation

cells differentiate

primary tissues with different function become obvious

primary structure of root 

1. epidermis - the outer layer of tissue in a plant

2. cortex - outer layer of cerebrum

3. stele - the central core of the stem and root of a vascular plant

parts of the cortex

1. exodermis

2. central cortex

3. endodermis

stele (vascular cylinder)

1. pericycle

2. xylem & phloem

Endodermis

the inner most layer of the cortex 

Casparian strips

band like cell wall structures made up of bands of lignin and suberin (located in the endodermis)

pericycle

delimits the stele from the endodermis

consists of a single layer of cells with thin, cellulosic walls

xylem and phloem

the roots form separate strands that alternate with one another.

number of xylem = number of phloem

protoxylem(px)

tracheary elements with small diameter develops

metaxylem (mx)

larger diameter

derived from protoxylem

name the elements in this photo

pericycle, metaxylem, protoxylem, primary phloem

name everything in this image

root hair, protoxylem, metaxylem, epidermis, pericycle, hypodermis, endodermis, cortex, protophloem, metaphloem

what are these?

Lateral roots

which primary structure is this?

monocot

what is this?

eudicot

this is a cross-section through the inner cortex and central cylinder (stele) of a root. what is indicated with arrows?

metaxylem

symbiosis

the host plant provides rhizobia with carbon and source of energy for growth while rhizobia fix atmospheric N2 and provide the plant with a source of reduced nitrogen in the form of ammonium.

symbiosis part A: nitrogen fixation by rhizobia

1. roots produce flavonoids/isoflavonoids

2. rhizobia produce Nod Factors

3. Infection thread in root hair

Mycorrhiza

mutualistic relationship between a plant (through its roots) and a fungus.

Ectomychorrhizas (mostly in trees)

• have a manthle consisting of a dense network of hyphae

• hartig net of hyphae surrounding the plant cells within the root cortex

Endomychorrhizae

fungi will penetrate inside the root cortex cells

mycoheterotropic plants

use the underground mycorrhizal networks of green plants to acquire photosynthetically fixed carbon

• parasitic 

This is a fragment of the root of a plant from the legume family (Fabaceae). What are the structures on the root?

a. Nodules with rhizobia

b. Nodules with  mychorrhiza

c. Just some warts

d. Nodules with nematodes

e. Little potatoes

nodules with rhizobia

The structures on the root of a plant from the legume family (Fabaceae) are nodules containing rhizobia. Rhizobia are nitrogen-fixing bacteria that form a symbiotic relationship with legumes, helping the plant to convert atmospheric nitrogen into a form that the plant can use.

Knowing that the fungal hyphae around this root do not penetrate inside the root cells, this is/are…

a. Endomycorrhiza

b. Arbuscular mycorrhiza

c. Ectomycorrhiza

d. Root nodules

c. Ectomycorrhiza
The question pertains to the type of mycorrhizal association where fungal hyphae surround the root but do not penetrate the root cells. This description matches ectomycorrhizae, where the fungal hyphae form a sheath around the root without penetrating the root cells.

food storage roots

have evolved to develop a hypertrophied storage parenchyma 

water storage roots

super developed parenchyma is storing water

propagative roots form adventitious buds

plants can propagate themselves vegetatively using these roots

• always perennial, herbaceous, or woody

Pneumatophores

specialized aerial roots that evolved in certain plants growing in swamps and marshes for gas exchange

prop roots

aerial roots that have an adentitious origin on the stem but they grow down and root in the soil, anchoring the plant

Buttress roots

aerial roots with a support role; they are encountered in some tropical tree species

epiphyte

A plant that grows on another plant and depends on it for support but not for food

• get water and nutrients from the air and water

photosynthetic roots

aerial roots of many epiphytic plants can photosynthesize at the same time with absorbing water from air.

“climbing” roots

Aerial, adventitious roots of lianas

contractile roots

characteristic to underground stems such as bulbs, corms, and rhizomes

parasitic roots = haustoria

taking water and nutrients from their hosts using a specialized organ called haustorium